A study published in this week’s issue of the New England
Journal of Medicine suggests that repeated topical use of
products containing lavender oil and/or tea tree oil may cause
prepubertal gynecomastia, a rare condition resulting in enlarged
breast tissue in boys prior to puberty, and for which a cause
is seldom identified.

Researchers at the National Institute of Environmental Health
Sciences (NIEHS), part of the National Institutes of Health (NIH),
confirmed in laboratory studies what a pediatric endocrinologist
at the University of Colorado at Denver and Health Science Center’s
School of Medicine suspected after diagnosing three of his young
male patients with prepubertal gynecomastia. The researchers found
an association between the use of products containing these oils
and the rare disorder, but cautioned more research is needed. At
this point, the findings are only applicable to young males with
unexplainable enlarged breasts who are regularly using products
containing these essential oils.

"We want to encourage doctors who may be seeing patients with
gynecomastia to ask their patients about the products they are
using. Patients with prepubertal gynecomastia may want to consider
reducing the use of products that contain these oils,” said Ken
Korach, Ph.D., chief, Laboratory Reproductive and Developmental
Toxicology at NIEHS and author on the study. “Although we found
an association between exposure to these essential oils and gynecomastia,
further research is needed to determine the prevalence of prepubertal
gynecomastia in boys using products containing lavender and tea
tree oils. Results of such epidemiological studies are important
to tell us how strong the association is between topical application
of the oils and prepubertal gynecomastia”

The three otherwise healthy Caucasian boys, ages four, seven and
10 years, had normal hormonal levels when they were diagnosed with
gynecomastia by Clifford Bloch, M.D., in Colorado. All had either
used lavender-scented soap and skin lotions, or shampoos or styling
products that contained tea tree oil and lavender oil as ingredients.
In each case, several months after the suspected products were
discontinued, the gynecomastia had subsided or resolved.

After Bloch discussed the cases with Korach, the NIEHS researchers
conducted experiments using human cells to determine if the oils
mimic the effects of estrogen, the female hormone that stimulates
breast tissue growth, or inhibited the effects of androgen, the
hormone known to control masculine characteristics and inhibit
the growth of breast tissue. The researchers tested the ability
of the oils to modulate or inhibit gene expression.

“The results of our laboratory studies confirm that pure lavender
and tea tree oils can mimic the actions of estrogens and inhibit
the effects of androgens,” said Korach. “This combinatorial activity
makes them somewhat unique as endocrine disruptors.”

Bloch said the laboratory studies support his hypothesis. “Since
there was no identifiable cause for prepubertal gynecomastia in
the three patients we reported, we speculated that environmental
factors might be contributing to their condition. Together, the
case histories and NIEHS in vitro studies provide support
for our hypothesis that topical exposure to lavender and tea tree
oils likely caused gynecomastia in the three patients.”

The oils did not alter the levels of the usual forms of circulating
estrogens and androgens in the boys. “We do not anticipate any
long term effects on hormonal levels,” said Derek Henley, Ph.D.,
the lead NIEHS author on the study. It is unknown whether the oils
have similar endocrine disrupting effects in prepubertal girls,
adolescents or adults.

These essential oils might now be considered endocrine disruptors
since they appeared to have caused an imbalance in estrogen and
androgen signaling. Endocrine disruptors are naturally occurring
compounds or synthetic chemicals that may interfere with the production
or activity of hormones of the endocrine system leading to adverse
health effects.

The National Institute of Environmental Health Sciences (NIEHS),
a component of the National Institutes of Health, supports research
to understand the effects of the environment on human health.
For more information on environmental health topics, please visit
our website at http://www.niehs.nih.gov/.

The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov.